Biomimetic aggrecan molecularly engineers articular cartilage fallowing intra-articular injection in an OA rabbit model in vivo: a pilot study

摘要

Introduction: Several biomolecules are depleted in osteoarthritis (OA) including hyaluronic acid (HA) in the synovial fluid and aggrecan in articular cartilage. Intra-articular HA injections have been widely used in an attempt to restore joint lubrication and reduce cartilage erosion, however they have had limited success. Our lab has synthesized a novel biomimetic aggrecan (BA) aimed to infiltrate and distribute In articular cartilage delivered via an intra-articular injection'2'. BA mimics the 3-D bottle brush structure and properties of naturally occurring aggrecan and consists of a poly(acrylic acid) (10kDa) core with chondroitin sulfate bristles. BA is intended to restore hydration and mechanical function to arthritic cartilage by molecularly engineering tissue without relying on cellular synthesis to regenerate the extracellular matrix. Here we investigate the effect of intra-articular injections of BA into normal and arthritic rabbit knee joints by determining the histological response of articular cartilage to BA and quantifying the coefficient of friction of the rabbit knee joint. Materials and Methods: ACL Transection (ACLT) was used to create osteoarthritis in the right hindlimb of 4 female New Zealand white rabbits while the left hindlimb served as a control (IACUC approved pilot study). These rabbits formed 2 groups: 1) ACLT and 2) ACLT + BA. Five weeks after surgery, the two rabbits in the ACLT+ BA group underwent weekly injections of BA for 3 weeks. Two additional non-ACLT rabbits underwent BA injections in the right hindlimb once weekly for 3 weeks. The contralateral hindlimb of these two rabbits had one injection of fluorescently-labeled BA two days prior to sacrifice. Immediately after euthanasia, the limbs were tested in a custom pendulum friction tester to measure joint friction and then prepared for histology or fluorescent imaging. Results: Osteoarthritic rabbit knees treated with BA exhibited a lower coefficient of friction than OA knees alone. The rabbit knees which only received BA injections exhibited almost the same coefficient as the control knees. A more robust articular cartilage layer is present in arthritic specimens treated with BA than arthritic specimens with no treatment. Confocal microscopy of fluorescently labeled BA injected knees showed fluorescence within the articular cartilage. Discussion: The results from our pilot study provide preliminary data to support the ability of biomimetic aggrecan to molecularly engineer osteoarthritic cartilage through cartilage. Our preliminary findings on joint friction indicate that BA has no adverse effect on joint coefficient of friction and may help to reverse the increased friction that resulted from OA. A study using the same model is currently underway with a group size of five. Conclusion: Our pilot results indicate that BA decreases the coefficient of friction of the osteoarthritic knee and increases the cellularity and thickness of the articular cartilage, supporting our hypothesis that BA can provide increased hydration to the joint and regenerate superficial layers of articular cartilage.